Researchers have discovered a genetic marker that could help to predict the risk of an unexpected premature birth.
Prematurity is linked to health problems
The discovery might also explain why African-American women seem to be more at risk of having a premature birth than their white counterparts.
US researchers found African-American babies were three times more likely than babies of European descent to carry the key genetic variant.
The study appears in the Proceedings of the National Academy of Sciences.
Premature babies face a greater risk of a range of health problems, including learning difficulties, respiratory disorders and vision and hearing loss.
There are several factors that can help predict the risk of a premature birth.
However, until now there has been no known cause for around half of all cases.
If doctors could be given advanced warning of the possibility that a woman will deliver early it would enable them to tailor their treatment accordingly, and take measures to minimise the risk of an early birth.
Dr Jerome Strauss, from Virginia Commonwealth University, examined a gene called SERPINH1 which controls production of the protein collagen, a key component of many body tissues, including cartilage, ligaments, tendons, bone and teeth.
He identified a variation of the gene which caused it to produce reduced amounts of collagen.
This could be key in pregnancy as it could lead to weakened foetal membranes, increasing the odds of them rupturing, and triggering a premature birth.
Dr Strauss said: "This is an example of how heredity may play a role in pregnancy complications and how genetic factors can contribute to racial disparities in the incidence of pre-term birth.
"With better understanding of this genetic variation, we hope to be able to identify pregnancies at greater risk of pre-term birth and intervene to prevent it."
Professor Lucilla Poston, from Tommy's, the baby charity, said previous research had suggested genetic factors were a factor in pre-term births - but not necessarily a strong one.
"This recent study is exciting, as it has shown a strong relationship between this gene and instances of premature birth.
"However, the numbers studied were small and as in all studies of this kind, we must await investigation in much larger populations to confirm the observation."
A spokesman for Bliss, the premature baby charity, said 45,000 babies were born prematurely every year in the UK.
"If we are able to increase the amount of time these vulnerable infants spend within their mother's wombs, we may be able to improve survival rates and outcomes for these babies."
Separately, Dr Xiaobin Wang, of Chicago's Children's Memorial Hospital, found a genetic variant of a gene called prolylcarboxypeptidase had a significant link with the pregnancy condition pre-eclampsia.
The only sure way to stop pre-eclampsia developing into a life-threatening condition is to deliver the baby as soon as possible - usually by a Caesarean delivery.